Roller apparatus for stretching film webs



March '10, 1970 w. J SCHMIDT ETAL 3,499,185

ROLLER APPARATUS FOR smmqnme FILM WEBS 1 Filed May 6, 1968 2 Sheets-Sheet 1 FIG] INVENTORS WILLI J. SCHMIDT WALTER SEIFRIED BY WMW ATTORNEYS March 19, I970 w. J. SCHMIDT ET AL 3,499,185

ROLLER APPARATUS FOR STRETCHING FILM WEBS Filed May 6, 1968 2 Sheets-Sheet 2 INVENTORS J. SCHMIDT R SEIFRIED United States Patent Int. (:1. tube 17/02 US. Cl. 18-1 9 Claims ABSTRACT OF THE DISCLOSURE A pair of idler rolls are mounted for rotation in a defined distance about fixed spaced parallel axes. A driving roll is supported by said idler rolls and is mounted in a bearing between said idler rolls for rotation on the axis of symmetry which is parallel with those of the idler rolls. The driving roll defines a nip with each of said fixed idler rolls. Drive means is connected over a suitable hinge coupling with the driving roll. A movable idler roll is disposed for rotation on or near the axis of symmetry which is substantially parallel with said aforementioned axes and is further mounted on the movable end of a rocking lever (swing beam) for pivotal movement toward the driving roll so that when the movable idler roll is in operative position to define a nip with said driving roll, it is disposed with its axis of rotation lying substantially in the longitudinal plane of symmetry of the axes of the other rolls. A web extends around the rolls in such a manner that the force necessary to exert pressure at the roll nips is derived from the tension in the web material.

The present invention relates to roller apparatus especially adapted for stretching film webs wherein the film may be formed of plastic or the like, and this roller apparatus may also be employed to stretch webs in various applications in other fields if so desired.

For the longitudinal stretching of web material, for example plastics film, it is known to use groups of rolls which contain two or more rolls in a group. The geometrical arrangement of the rolls varies. The underlying principle depends upon the exerting of pressure, between the roll nips, by means of an external force. The main cause of trouble in the use of such apparatus is bending of the roll surface at the nip owing to the external force. In the case of more than two rolls, the difference in their speeds, due to the use of a separate drive for each roll, is a further factor leading to unreliability. When the web is under heavy stresses such as occur for example in the stretching of plastics film material, it is often not possible to adapt the applied pressure to the tension in the web. This leads to partial or total slipping of the web in the nip. It is therefore generally necessary to subject the web to a strong exit tension, by means of equipment located in advance of the roll assembly, in order to compensate for the fact that the rolls do not grip the web material sufiiciently,

The present invention provides a roll assembly, for use more especially for stretching webs of plastics film, said assembly including a pair of idler rolls rotatably mounted 3,499,185 Patented Mar. 10, 1970 on fixed parallel axes spaced to support between them a driving roll, and above the driving roll a movable idler roll on a further parallel axis, said movable idler roll being mounted to pivot toward and away from the driving roll that it can form a nip therewith in a position in which the imagined reference axis is the vertical plane of symmetry of the roller arrangement (grouping), the arrangement for passing a web between the rolls being such that the web can be introduced onto or removed from the upper surface of the said movable idler roll on the side of its axis opposite to the side on which its pivot is located, in a path which approaches but is spaced from the periphery of the adjacent fixed idler roll, and the web can pass, in one direction, around the said movable idler roll, through a nip between it and the driving roll, then through a nip between the driving roll and the said adjacent roll of the lower pair, under the driving roll, through a nip between it and the other roll of the lower pair and out of the assembly over the top of the said other roll or, in the opposite direction, in the reverse sequence.

In a modified form of roll assembly according to the invention, the said movable idler roll is replaced by a pair of spaced further rolls each similar to the said movable idler roll except that they are pivoted on a common axis that is itself in the said longitudinal plane of symmetry and that their axes in their nip positions have a plane of symmetry that substantially coincides with said longitudinal plane of symmetry, in this case the arrangement for passing a web between the rolls being such that the web, after similar introduction onto either of the pair of fixed idler rolls, passes through a nip between it and the driving roll, then through a nip between the driving roll and the said adjacent roll of the lower pair, under the driving roll, through a nip between it and the other roll of the lower pair, through a nip between the driving roll and the other of the said pair of further rolls and out of the assembly by a similar path to its path of entry.

In a roll assembly according to the invention, the roll surfaces do not bend at the nip and there is no difference between the speed of opposed rolls at the nip and the speed of travel of the web material passing between them and accordingly the web does not slip or ruck up between the two rolls.

The arrangement according to the invention enables the forces necessary to exert pressure at the roll nips to be derived from the tension in the web material. In particular, by the selection of the angle at which the web material enters on the tension side and by the selection of the position of the pivot point for the movable idler roll, it is possible to establish a proportionality factor which itself determines the required factor of multiplication of the forces occurring as tension for conversion into pressure forces.

The following advantages are obtained from using the roll arrangement according to the invention:

(a) Based on the tensile force (web tension) in the material being processed, positive tension adjustment with proportionality factor n that can be determined by structural geometry.

(b) Complete independence upon external force: the roll pressure forces, uniformly distributed over the width, can be obtained from the web tension as directly acting components, whereby any negative curvature of the roll body (i.e. curvature causing a gap to form in the middle) 3 is avoided and an even pressure is applied over the entire width of the web.

(c) By grouping idling rolls, for example three of such, about one central driving roll, automatic adaptation of each nipping point to the speed difference in the various stages of elastic deformation.

(d) An effective system is provided Without any practical limitations even when the Web tension in the direction opposite to the tension side is zero (complete separation of tension zones) or when sudden stress peaks occur on the tension side.

The roll arrangement according to the invention fulfills a long-felt Want and, using readily controllable and technically available means, ensures safe and reliable operation even in the case of difiicult fields of application.

The invention is illustrated by way of example in the accompanying drawings, in which:

FIG. 1 is a perspective view of one embodiment of a roll arrangement according to the invention,

FIG. 2 is a side elevation of the arrangement of FIG. 1.

Force diagrams, corresponding to the tension conditions in the static state, have been included in FIG. 2.

FIG. 3 is a side elevation of a second embodiment and FIG. 4 is a side elevation, similar to that shown in FIG. 2, of two roll arrangements arranged consecutively.

Referring to the drawings, in FIGS. 1 and 2, 1 and 2 are freely rotatable reaction-absorbing idler rolls, mounted parallel to one another on fixed axes. A third roll 3, acting as driving roll and itself being driven by means of a suitable flexible coupling 25 from a motor 26, is mounted in a bearing 9 on an axis of symmetry a-b (see FIG. 2) passing between fixed idler rolls 1 and 2. In a section perpendicular to the three roll axes, lines joining them form a triangle having an apical angle a. of, e.g., 120 as seen in FIG. 2. A further parallel movable idler roll 4 is positioned over the driving roll 3, on or near the axis of symmetry a-b of the other three rolls, and the journals 5 of this roll 4 are mounted to be freely rotatable in the outer ends of levers 6 pivoted on pivots 7. The arrangement is such that lines from the pivot points at pivots 7 passing radially through the axis of the roll 4 meet the periphery on the further side of this roll at the point where an approaching web 8 meets this roll, the direction of this approach as indicated by arrow A being such that the web has just sufiicient clearance from the periphery of the roll 1. The path of the web 8 between the rolls is as shown and will be described in greater detail below.

The arrangement shown in FIG. 3 isolates two different or alternating Web-tensioning forces. A driw'ng roll 11 determines the speed at which the web passes through the apparatus, fixed axis rolls 16 and 17 serving to deflect the Web to achieve the most favorable approach angle of the web in each case. Fixed axis idler rolls 14 and 15 absorb the reaction forces. Movable idler rolls 12 and 13, mounted on levers 6 pivoted on a pivot 18, have a similar function, the roll on the side where the greater tensioning force occurs at any instant taking up the correspondingly greater proportion of the pressure.

FIG. 4 shows a mirror-image duplication of the roll arrangement illustrated in FIGS. 1 and 2. In this case, the Web is stretched between the roll groups, in the zone between defiecting rolls 19 and 20, under the action of heating means (not illustrated), the driving roll 22 of the leading roll group naturally having a greater peripheral speed, according to the stretching ratio, than the driving roll 21 of the trailing roll group, which latter roll therefore has a braking action. The positions of the pivotal centers 7, of movable idler rolls 23 and 24 enable pressure forces at the nips of these rolls with the rolls 21, 22 respectively to be exerted only when there is tension in the web between the rolls 18 and 20.

As can be seen from FIGS. 1 and 2, the Web 8, which is guided into the roll system at the desired angle, by means of usual guides and deflecting means (not illus- H first passes around the roll 4 and then passes .4 around thedriving roll 3, after which the emergingweb 10 continues its course from any required point on the periphery of the roll 2. It is obvious that when the web 8 is introduced, the rolls 3 and 4 are raised by known means, not shown in the drawings, e.g. hydraulic jacks, so as to facilitate the lead-in.

In all the figures of the drawings, to indicate the stress in the web, each tension side has been shown by an arrow marked with the tension P and it is important to note that the effective direction of tension must not be confused with the direction in which the Web 8 and 10 is travelling as indicated by arrows A in the various figures. In this connection, reference is made to FIG. 4, where in the combined method employing two groups of rolls, the direction of. travel and direction of tension are first identical but are opposite in the right-hand group of rolls.

As already mentioned, in FIGS. 1 and 2 the center roll 3 provides the drive and therefore also determines the speed at which the web travels through the rolls, and this roll, as required, is subjected to a correspondingly heavy torque. However, even in the static condition, an inherent automatic tensioning effect of the roll arrangement arises owing to the fact that the tension P present in the web material 8, acting on the roll 4, produces a force in the vertical direction, whereby the web passing between the rolls 3 and 4 is subjected to a corresponding pressure and the roll 3 is likewise loaded in the vertical direction. The web passes around the roll 3' to an extent such that it becomes located between the geometric points of contact of rolls 3 and 1 on the one hand and rolls 2 and 3 on the other. It can be seen, particularly in FIG. 2, that in the structural geometry, which later remains constant, a proportionality factor can be determined which, when multiplied by the variable tension P determines the sum of the pressure forces. The relationship is represented by the formula wherein P is the pressure at a nipping point, P is the tension in the web and n is the proportionality factor which, in the normal way, can be determined by a resolution of forces in accordance with graphostatics and/0r analytical calculation in a force diagram. Such a force diagram is shown in FIG. 2. An arithmetical example will be used to illustrate how the proportionality factor n can be arrived at: the tension P will be assumed to be 1000 kg. By combining the two tensions in the web 8, 10, a mean force P acting on the center of rotation of the roll 4, can be determined and introduced as a lateral force into a second force parallelogram to resolve the forces at the center of rotation of roll 4. (In the example a figure of 1700 kg. was determined for this force.) The second force parallelogram now gives the efiective vertical mean force P =1700 kg. Furthermore, the reaction forces are taken up by the fixed axis rolls 1 and 2. For determining the two equal lateral forces or reaction forces, the perpendicular force P is resolved in a further parallelogram starting from the center of the roll 3, each lateral force amounting to 1700 kg. It can be seen that due to the geometric arrangement selected in the example, three nipping points each with a load of 1700 kg., occur on the periphery of the driving roll 3, these thus jointly representing a total pressure of 5100' kg. Related to the tension P :1000 kg., the proportionality factor n is calculated, for example, as follows:

rolls and the angle of the entering film web are as illustrated in FIG. 2. To obtain a greater moment the pivotal center 7 should be displaced towards the line of symmetry a-b of the roll group (by this angular displacement, as seen in the relevant force parallelogram, the vertically acting mean force is increased) or if a change in this factor is desired in the opposite direction, said center is positioned further away from the line of symmetry. This displacement must, of course, be within the limits normally set by constructional requirements, since the entire possible range lies between an infinitely large moment (pivotal center 7 on the line of symmetry a-b) and a moment=0. The necessary degree of multiplication of the tension P in converting it into pressure forces can thus be selected in advance with considerable reliability and can be suited to the purpose of each intended use.

The roll arrangement according to FIG. 3, as above referred to, has two movable idler rolls 12 and 13, pivoted on the axis of symmetry a-b, the roll 12 or 13, subjected at any instant to the greater tensioning load, exerting the correspondingly greater proportion of the derived pressure forces.

A further feature of the roll arrangement of FIGS. 1 and 2 is the possibility of adapting the three non-driving rolls 1, 2 and 4 to the speed difference in the various stages of the elastic deformation. The following example will explain this procedure:

When stretching plastics film, the web 8 (on the tension side) is subjected, both in the deformable condition during the stretching process and after solidification, to a tensioning load of possibly several thousand kilograms, which load is naturally propagated as elastic deformation as far as the solidification stage and thus likewise extends to the first nipping point between the rolls 3 and 4. Assuming that beyond one or in front of another roll system, the web 10 is still under only a slight tension, sufiicient for transport (effecting complete separation of the tension zones) then, in practice, the total tension must be dissipated and the elastic deformation takes place on the path between the first nipping point of the rolls 3 and 4, and the third, last nipping point between the rolls 2 and 3, on the part of the circumference of roll 3 around which the web 10 passes. This leads to a stepwise differential of the speed of the web through the rolls at the nipping points, the idling rolls 1, 2 and 4 taking up the local speed of the web and the nipping points thus being uniformly loaded. The formation of loose folds (web no longer lying closely against the roll 3) or relative movement between web and roll at the nipping point (slip due to dilference in speed) cannot occur.

The fact that the roll pressure forces are independent of an external force is a further important feature of the roll arrangement according to the invention. For example, rolls 3 and 4 of FIGS. 1 and 2, in particular, are drawn closely together by means of the force which is derived from the web and is accordingly evenly distributed over the width of the web, these forces again fulfilling their irreversible function in the optimum zone of the whole web-width. A nip-closing effect is achieved, and the median portions of the web are loaded just as much as the marginal zones. Thus, this roll arrangement can also be used in cases of an unusually extended width (e.g. 3 meters), in which a thin web, only a few microns thick, is concerned and no slip can be allowed.

The roll surfaces should be of materials suitable for their individual tasks. It is of advantage to provide the driving rolls 3, 11 and 21 with a dimensionally stable surface (to achieve constancy of speed), for example a chromium-plated steel jacket, and to cover the idling rolls 1, 2 and 4 with an elastic layer, for example of rubber. However other roll surfaces and combinations. are also possible, these being selected with such factors in mind as grip, prevention of damage to the web, optionally ap- 6 plying markings to the web (by means of appropriately engraved rolls), high gloss elfect, matt finishing and so on.

It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. Roller apparatus for stretching film webs comprising a pair of spaced fixed idler rolls rotatably mounted at a defined distance on fixed substantially parallel axes, a driving roll disposed between said idler rolls and mounted in a bearing for rotation on an axis of symmetry disposed substantially parallel with said first mentioned axes, said driving roll defining a nip with each of said first mentioned fixed idler rolls, means for drivng said driving roll, a movable idler roll spaced from said first two idler rolls and rotatably mounted on or near an axis of symmetry substantially parallel with said aforementioned axes, and further mounted on the movable end of a rocking lever for pivotal movement toward the driving roll to define a nip therewith, said apparatus being arranged for receiving a web disposed adjacent one of said fixed idler rolls and extending over said movable idler roll, through the nip between said movable idler roll and said driving roll, around said driving roll, through the nip between said drive roll and said one fixed idler roll, under the driving roll and through the nip betweenthe driving roll and the other of said fixed idler rolls, whereby the force necessary to exert pressure at the nips between the rolls is derived from the tension in the material of the web associated with the rolls.

2. Apparatus as defined in claim 1 wherein when said movable idler roll is disposed'in the operative position to define a nip with said driving roll, the axisof rotation of said movable idler roll is disposed substantially in the longitudinal plane of symmetry of the axes of said driving roll and said fixed idler rolls.

3. Apparatus as defined in claim 1 whereima line extending from the pivot point about which said movable idler roll is pivotally mounted and passing radially through the axis of said movable idler roll intersects the periphery at the far side of the movable idler roll at substantially the point where an associated advancing web comes into contact with the outer periphery of said movable idler roll.

4. Apparatus as defined in claim 1 wherein said driving roll is supported by said fixed idler rolls with ,the axis of rotation of said driving roll disposed substantially in a plane of symmetry passing between said fixed idler rolls.

5. Apparatus as defined in claim 1 wherein said movable idler roll is disposed above said driving roll and when in operative position to define a nip with said driving roll has the axis of rotation thereof disposed substantially in the longitudinal plane of symmetry of the axes of said other rolls.

6. Apparatus as defined in claim 1 including an additional movable idler roll, each of said idler rolls being mounted for pivotal movement about a common axis which lies substantially in the longitudinal plane of symmetry of the axes of said fixed idler rolls and said driving roll.

7. Apparatus as defined in claim 6 wherein when said pair of movable idler rolls are disposed in their nip positions with respect to said driving roll, the axes of said movable idler rolls have a plane of symmetry that substantially coincides with the said longitudinal plane of symmetry.

8. Apparatus as defined in claim 1 including an additional roller apparatus which is a mirror image of said aforedescribed roller apparatus and wherein an associated web passes from the movable idler roll of one roller apparatus to the movable idler roll of the other apparatus.

9. Apparatus as defined in claim 1 wherein said driving roll is supported by said pair of fixed idler rolls with the rolls, said movable idler roll being disposed above said References Cited driving roll and being mounted for pivotal movement UNITED STATES PATENTS toward and awa from said driving roll with the axis of rotation of said movable idler roll when the idler roll godenacker' ash. defines 2. mp with said drivlng roll being disposed sub- 5 3 243 844 5/1966 Nash stantially in the longitudinal plane of symmetry of the 3:261:903 7/1966 Cam axes of said pair of fixed idler rolls and said driving roll. WILLIAM J. STEPHENSON, Primary Examiner 

